Fluoropolymers have excellent properties of chemical resistance, solvent resistance, heat resistance, and fouling resistance, and are therefore used as materials of various products effectively utilizing the properties, in a wide range of industrial fields such as the automobile industry, semiconductor industry, chemical industry, and coating materials.
These fluoropolymers are produced by emulsion polymerization, suspension polymerization, or solution polymerization of fluoroolefins. The emulsion polymerization usually utilizes surfactants. An increased amount of surfactant leads to a greater number of polymer particles generated in the initial stage of the emulsion polymerization, which increases the polymerization rate and improves the production efficiency of fluoropolymers. In the case of using a large amount of surfactant, however, the obtained fluoropolymer tends to show deteriorated properties (e.g. water resistance). For this reason, a production method has been desired which enables efficient polymerization in the presence of a small amount of surfactant and which does not adversely affect the properties of the fluoropolymer.
Based on such a state of the art, Patent Literature 1 proposes a method of producing a fluoropolymer in the presence of a linear aliphatic sulfonate surfactant in place of expensive ammonium perfluorooctanoate that is commonly used in emulsion polymerization of a fluoropolymer. This method actually has a problem that the number of particles of the fluoropolymer generated is small.
Patent Literatures 2 and 3 propose a production method utilizing an alkyl phosphoric acid or an ester thereof as a non-fluorinated surfactant. Patent Literature 4 proposes a method utilizing a compound in which phosphoric acid, sulfonic acid, carboxylic acid, or the like acid is bonded to quaternary carbon atoms.